Identifier

Author

Degree

Master of Science (MS)

Department

Dairy Science (Animal, Dairy, and Poultry Sciences)

Document Type

Thesis

Abstract

Lactose sugar is a source of energy for Lactic Acid Bacteria (LAB) in dairy fermented products. Enrichment of yogurt with lactose addition may increase growth and viability of the yogurt starter culture (Streptococcus thermophilus and Lactobacillus delbrueckii ssp. bulgaricus) and enhance yogurt physico-chemical and sensory attributes. The objectives of this study were: to determine the influence of added lactose on (1) acid and bile tolerance of yogurt starter culture Streptococcus thermophilus ST-M5 and Lactobacillus bulgaricus LB-12, (2) the final lactose content of yogurt during its shelf life, (3) the physico-chemical characteristics of yogurt during shelf life, (4) the growth of the yogurt starter culture during yogurt´s shelf life and (5) the sensory attributes of yogurt. Acid tolerance test was conducted on pure culture at 30 minutes intervals for 2 hours of incubation period and bile tolerance at 1 hour intervals during 12 hours. Fat free plain set-type yogurt was manufactured using 0, 1, 3 and 5% w/w added lactose to accomplish objectives 2, 3 and 4. For objective 5, a blueberry yogurt was manufactured using the same lactose levels. Analyses for plain set-type yogurt were done at 7 days intervals during 35 days of storage period. Sensory evaluation was conducted on yogurt 3 days after its manufacture. Data were analyzed using Proc Mixed model of SAS® 9.3 program and by analysis of variance (ANOVA) using Proc GLM. Significant differences between means were analyzed at α = 0.05 using Tukey´s adjustment. Lactose had a positive effect on acid tolerance and bile tolerance of both yogurt starter cultures, growth of S. thermophilus and sensory attributes of flavored yogurt. Mean overall liking scores were higher for samples containing added lactose compared to control as tested by 100 panelists. Lactose supplementation in yogurt might be a good approach to increase its health benefits, acceptability and purchase intent among consumers.